Method of preparing catalytic agents



i 7 '0 all whom it may concern:

Patented Mar. 16, 1926. 7 h

' UNITED/"S A ES- PATENT OFFICE.

WALTER A. PATRICK, or morm'r wnsnmeron', MARYLAND, ASSIGNOR 'ro'rnnSILICA GEL CORPORATION, or BALTIMOBE,-MARYLAND, A 'conronnrron orMARYLAND.

METHOD OF PREPARING CATALYTIC AGENTS.

No Drawing.

Be it knownthat I, WALTER A. PA'rmoK, a citizen of the United States,and residing at Mount Washington, Baltimore County,

State of Maryland, have invented certain new and useful Improvements inMethods of Preparing patalytic Agents, of which the following is a.specification.

The present invention relates to methods of preparing catalytic agents"comprising active material or catalysts proper associated withcarriers. vThis application is a continuation in part of-my application,Serial No. 467,311, filed" May 6, 1921.

The present method gives a catalytic mass which is particularly suitablefor gaseous reactions although it' is not limited to such uses, as itmay be applied to other catalytic reactions' It may be used in lump oranular form or in a more subdivided condition, as may be founddesirable.

Frequently, and especially when the active material is'costly, as whenplatinum is used, it is desirable to prepare the catalytic mass in sucha way. that the maximum amount of the active material used shall beequally available and capable of functioning to its maximum efiiciency.It is one of the objects of the resent invention to at:

'tain this result, T e active material'after' being. associated with thecarrier is in such physical condition that it presents an unusuallylarge surface per unit of weight, and

the entire amount thereof is deposited on the surface of the pores at orvery near. the external surface of the carrier, sothat all of the activematerial is 'elfective onithe reacting substances, when the latter arepassed through the catalytic bed or otherwise brought into contact withthe catalyst.

The foregoing and other objects are accomplished by using a "carrierwhich possesses the necessary ph sical structure; and also following themeth of depositing the'active material thereon.

The material employed ascarrier according to the present invention musthave a large number of ultra-microscopic pores.

They are so small that it-is diflicult to 've a satisfactory measure oftheir size. ow-' ever,-for all praoticalpurposes, the amount of waterpresent in the porous carrier when it is in equilibrium with water vaporunder 0d described herein Application m d November 1s, 1a2 2. Seria1N0.801,867.

given conditions of temperature and partial pressurewill give a measureof the size of the pores, since the amount of water present in thecarrier-is a function of the size no pores'as small as the greater partof the V ores in silica gel. On the other hand highy activated charcoalcontains more water than silica gel under these conditions, whichindicates that it has more small pores'than sllica gel.

Many products that are improperly termed gels do not have the structureto absorb at these low partial pressures. I Thus, the product obtainedby precipitating silicic acid by mixing sodium silicate and an acid anddrying the precipitate, does not have the finely porous structurerequired It is porous but the pores are not small enough.

On the other hand, silica gel such as obtained as the product of themethod disclosed in my Patent 1,297,724; has the required structure.

The physical structure of the carrier-is of importance because it is oneof the fac tors which determine the extent of. subdivision of thecatalyst deposited thereon and. Y i also the extent to which the entirequantity I of catalyst used is able -to function at its maximumefliciency. I have 'discovered that silica gel, having the pore sizedefined above after being impregnated with a catalyt1c' materialproduces a catalyst many times as eflicient per unit weight of. activematerial as the ones now employed. g

No. 362,138, filed Inmy application Serial February 28, 1920, I havedisclosed and claimed methods of preparing catalyzers of the typementioned above. The product as a new composition is 'claimed'mapplication 'Serial No;

15,727, a division of said appli cation Serialhlo. 362,138. In myapplication Serial lilo. 466,998, filed May 5, 1921, I have disclosedand claimed anothermethod of preparing such catalyzers. The methodscovered by the said application, 362,168, consists in the preparation ofthe catalytic gel by combining with materials from, which the gel isobtained, a substance or substances which will produce or give thecatalytic material in intimate association with the gel; while themethod set forth in application 466,998, consists in preparing thecatalyzer by treating the gel in substantially its final state ofmanufacture.

The present invention relates tomethods of this latter class, accordingto which the catalytic material is applied in colloidal form to the gelitself, and the resulting substance heated to expel the liquidassociated with the colloid. Since a colloidalsolution is employed inwhich the active material or the material which is to become active, andwhich is generally a metal or a metal oxide, is'a1ready in highlydispersed condition, the active material after deposition on thecarrier, is in extremely finely divided condition.

Any suitable active material may be used,

preparation of catalysts.

Methodsof pre aring colloidal solutions of metals and 0 metal oxides,are well known, as is shown-by Svedbergs Herstellung Kolloider Loesungen(anorganische Stofi'c) published by Theodor Steinkopff, Dresden, whichis devoted to general and specific methodsof preparing colloidalsolutions, such as of the metal themselves, or

their oxides, etc.

When a gel such as silica gel, the pores of which are already filled orsubstantially filled with water is brought into contact with a colloidalsolution of a metal or metal oxide in water so that the entire surfaceis wet with the solution, the colloidal particles will tend to difiuseslowly into the water within the gel pores. The depth to which thecolloidal particles will penetratewill depend extent. If, however, as isthe case with many colloidal solutions, .the particles are comparable insize with the diameters of mamas the pores, they will beheld in thepores at or very near the exterior surface, and in defined above, whichhas either been incompletely dried or after drying to about 3 to 12%water content has been allowed to take up water vapor until the poresare filled or nearly filled with water. In the case of silica gel havingthe pore size as defined herein this means a total .water content ofabout 30% to 40%. The gel is then brought in contact with a solutioncontaining a catal stin colloidal form, generally in water, and allowedto stay in contact for a suitable time, usually only a few minutes,whereupon the excess solutioni's drawn off and the residue of gel withits adhering catalyst is heated to reduce the water content. Should thecolloidal solution employed contain other substances than the colloidand which may be undesirable and non-volatile, the gel mass aftertreatment with the colloidal solution may be washed with a solvent,generally ater, before drying, or it may be washed thereafter.

he object of filling the pores of the gel with water before treating itwith the colloidal solution is two-fold. 'In the first place, if the gelis not already approximatey saturated with water, the rapid adsorptionthereof which'will' take place on contact with the solution will causethe gel granules to shatter into small fragments, which generally isundesirable but not always so. It should be noted in this case that noessential change takes place in the gel structure other than thereduction in the size of the granules.

Secondly, if the gel be not first saturated with water there will be agreater penetration of the catalytic material thereinto, particularly ifthe colloidal particles are relatively small, and that part of theactive ma terial which has penetrated to any appreciable depth withinthe granules will ave less chance of contact with the reagents and willtherefore be less efiicient than material which is at or near thesurface, whereby the efficiency of the material as a whole willbe'lessened. This is a matter of great importance with expensivecatalysts. On the other l1and,-'if the gel is saturated with waterbefore contact with the colloidal solution, the colloid can get into thegel only by the slow process of diffusion and consequently thepenetration intothe interior will be very slight.

It will thus be apparent that the use of a saturated, or almostsaturated, gel, has

certain important advantages, but where i such advantages are notessential, an unsaturated or fairly dry, or even a dry gel may be used.4

As one example of theapplication of my invention I will cite thepreparation of platinized silica gel for use as a catalyst for theconversion of sulphur dioxide to sulphur trioxide.

A colloidal solution of platinum is re-,

pared by the well known process of re uc "ing chlorplatinic aciddissolved in water, by

' means of formaldehyde. The platinum content of the solution may be0.314 grams per litre. This colloidal solution is poured over silica gelsaturated as described above, in

the proportion of 6.3 cc. of solution (containing 0.002 grams ofplatinum) to 20 grams of dry gel, the mixture being stirred of thecatalyst at the rate of 300 cc. per

minute 90% more or less conversion to S0,,

is obtained.

The activity of the mass per unit weight of platinum is many times asgreat as the activity of catalytic. masses heretofore used.

.This great activity seems to be due to the fact that when the platinumis deposited from a colloidal solution of the metal upon 1 a carrierwhich possesses a physical structuresuch as that of silica gel, it isnot only all deposited where it is most effective, but' the deposititself appears to possess as a solid, a degree of dispersion com arableto the colloidal state, and it accor mgly has the highest degree ofactivity as a catalyst.

Platinum impregnated silica gel has been cited as one application ofthis invention but it is to be understood that the invention is notlimited thereto. Any gel having'the structure previously defined may beemployed and may be impregnated as described with anymetal or metaloxide 101' with two or more of the same,.or with other material capableof forming acolloidal solution and the latinized gel to the particularreaction capable thereafter of acting as, orof being transformed into,catalytic material. Nor is the invention limited in the use of citenamely, to the conversion of sulphur dioxide to sulphur trioxide; butit, as well as other catalysts prepared according tothis process, areapplicable to a large number of other reactions. I p

Thetime ofcontact of'the gel with the colloidal solution used, which isnecessary or. suitable to give the best results, is of course, variableand depends upon the size and mass of the colloidal particles, the rateof diffusion of the same, and'the depth of penetration desired. Theconditions of heating the impregnated gel to complete the drying processmay be the same as are set forth in my Patent 1,297,724 for drying thesilica gel itself exceptin so far as modifications may be desirable forthe purpose of volatilizing or otherwise removing foreign 76 substanceswhich may have been present in a the colloidal solution used.

The platinum impregnated substance. is

claimed in application Serial No. 466,998.

Having thusdescribed the invention what 80' is claimed as new anddesired to be secured by Letters Patent is: 4

1. The process 1 of preparing a catlytic agent, consisting in treating aporous gel having pores ofsuch a size that the water content-at-30 C.when in equilibrium with water vapor at a partial pressure ofsubstantially 22' mm. of mercury will be at least 21% of the weight ofthe gel, .tlle pores of which at the time of treatment are substantiallyfilled with water, with a'colloidal solution of catalytic material, andremoving the water. l v i 2. The process of preparing a catalytic agent,consisting in treating a porous gel 5 having pores'of such a slze thatthe water water vapor at a arti 1 pressure of sub content at 30 C. whenn equilibrium'with o meriury will be at least stantially 22 mm.

21% of the weight of the gel the pores of which at the time of treatmentare substantially filled with water, with a colloidal solution ofcatalytic material, and evaporating the water.

3. The process of preparing a catalytic agent, consisting in treatin aporous silica gel having pores of such a size that the water content at30 C. when in equilibriumwith water vapor at a partial pressure ofsubstantially 22 mm. of 21% of the weight of the gel thepores of whichat the time of treatment are substantially filled with water, with acolloidal solution of catalytic material, and removing the '1'- 4. Theprocess of preparmg a catalytic. I

water.

agent, consisting in treating a. porous silica.

gel having pores of such a s1ze'that t he water content at 30 0. when inequ1l1b= mercury will be at least 1 rium with water vapor at a partialpressure of substantially el, the pores of which at the time oftreatment are substantially filled with water,

22 mm. of mercury will be at least 21% .of the weight .of the with acolloidal solution of catalytic matcrial, and heating to evaporate thewater.

5. A catalytic agent comprising porous gel having pores of such a sizethat thewater content at30 0. when in-equilibrium with water vapor at apartial-pressure of 3 substantially 22 mm. of mercury will be at least21% of the weight of the gel carrying a catalytic substance on thesurface only of the pores at and immediately adjacent the externalsurface of the gel particles.

6. A catalytic agent comprising porous silica gel having pores of such asize that the Water content at 30 0. when in equilibrium with watervapor at a partial pressure of least 21% of the weight of the gel,carrying a catalytic material on the surface only 01' the pores at andimmediately adjacent the external surface of gel particles.

In testimony whereof I hereunto aflix my 16 signature. V I

WALTER A. PATRICK.

